Thoughts from Starlight Cascade

In the midst of a lot of cloud, there opened up a 90 minute window on Tuesday morning of clear skies.
This was the first image of 37 runs, at 09:34UT or 04:34 EST. The Great Red Spot is showing nicely.

A curiousity… the first image was the best. Time to start wondering about the thermal dynamics of the system. The scope is outside in a metal observatory.. at ambient temperature with the inside of the observatory and maybe a little bit warmer than outside.
We open the roof.
I imagine that the OTA starts to cool a little more, maybe 1 or 2 C. It was about -2C outside at the time. The dew heater on the corrector plate was also turned on at the start, to about 50% duty cycle.
So… Is the worsening focus for the next 90 minutes a result of:

Increasingly worse skies?
The OTA continually cooling and not reaching equilibrium with the outside air temp and radiant cooling?
Is there too much unneeded heat coming off the dew heater and is that affecting the optics?

Statistically I find it hard to believe that the first image should be the best. All else being equal, the sky conditions should have given me something good in the 37 runs over 90 minutes, aside from the first.

The OTA would cool down further once the roof was opened… but that should not take more than 10? 20? minutes… it is mostly there already temperature wise.

Can a dew heater running too hot affect optics and focus?

Some interesting questions. To find out the answers I will, next time:
Open the roof and not image for 10 minutes
Take out a remote temperature meter and check the OTA temp every minute from opening until 1st image and then every 10 minutes later.
Not turn on the dew heater until 1/2 way through the session.

Processing is not yet complete for the animated .gif below… it will be replaced with an updated file when done.

After a few years of imaging now, I have gone through a few variations of recording image data. I’ve made up a new template to try out now as well… something to help remind me what needs to be recorded.
For instance, this morning:
Weather: -2C with winds 2-5 kph from SW
Moon was 24 days old and < 15 degrees from Jupiter Observatory: roof was stuck, needed some hitting with heavy object Telescope: using dew shield, no heater, x2 barlow Seeing: poor to average, Transparency average Computer - could not connect to scope, restarted, now connected and autoguiding with firecapture. Also started to use a new nomenclature on the files, to help remember the most important bits, like exposure in milliseconds, percent of frames used, altitude of Jupiter in degrees and Diameter of Jupiter in arcseconds. The Moon Io is just off to the upper right. No GRS seen.

Surprisingly, it was “clear” again this morning, against all predictions from last evening.

Rolled outside around 05:15 EST to low level fog and -5C and a frozen stuck roll off observatory roof.

A little bit of grunting got that open. The laptop was still up and running well. On powerup the 20cm LX200GPS display displayed garbage and was unresponsive. Cycled the power and this time it came up “normal” but of course, since it was not “parked” on the last power up, it wanted to do a full blown alignment. I declined and told it to find Jupiter anyways. It was not too bad… within .5 degrees. Put in a low power eyepiece to centre jupiter and then the ASI 120MC camera again.

Only had time for three 120second runs this morning. The first was without firecapture’s “autoalign” feature, where it keeps the image centered whilst the real object is bouncing around. It makes the stacking process better later on. The 2nd and 3rd runs had it on but the tracking had issues on the 3rd run and it was discarded.

Seeing was surprising average as was transparency, as evidenced by a 40ms exposure time.

This is the best 50% of the 2965 frames taken with Jupiter at 28 degrees altitude. Even with realtime focussing looking iffy, I was hoping for good images because of the stability or the air. Subtle cloud variations came out in post processing, which was great.

There was/is a single moon in the image, to the upper right, which I used to focus on with a 200ms exposure (just to see it better).

Stellarium tells me this is Io, with the other three Galilean moons on the other side of Jupiter and further out of frame. No Great Red Spot is apparent.

FYI The Perijove of the spacecraft Juno is Scheduled for Sunday 2016 Dec 11. Any observations or better yet imaging around that time might be useful!